Applications/Zlib
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Application Details
- Description: zlib is a software library used for data compression.
- Version: 1.2.8 (compiled with gcc)
- Modules: zlib/gcc/1.2.8
- Licence: Free and open source
Usage Examples
zlib is designed to be a free, general-purpose, legally unencumbered -- that is, not covered by any patents -- lossless data-compression library for use on virtually any computer hardware and operating system. The zlib data format is itself portable across platforms. Unlike the LZW compression method used in Unix compress and in the GIF image format, the compression method currently used in zlib essentially never expands the data. (LZW can double or triple the file size in extreme cases.)
A code example is shown below, using zlib
#include <stdio.h>
#include <zlib.h>
#include <stdlib.h>
#include <string.h>
/* CHUNK is the size of the memory chunk used by the zlib routines. */
#define CHUNK 0x4000
/* The following macro calls a zlib routine and checks the return value. If the return value ("status") is not OK, it prints an error message and exits the program. Zlib's error statuses are all less than zero. */
#define CALL_ZLIB(x) { \
int status; \
status = x; \
if (status < 0) { \
fprintf (stderr, \
"%s:%d: %s returned a bad status of %d.\n", \
__FILE__, __LINE__, #x, status); \
exit (EXIT_FAILURE); \
} \
}
/* These are parameters to deflateInit2. See
http://zlib.net/manual.html for the exact meanings. */
#define windowBits 15
#define GZIP_ENCODING 16
static void strm_init (z_stream * strm)
{
strm->zalloc = Z_NULL;
strm->zfree = Z_NULL;
strm->opaque = Z_NULL;
CALL_ZLIB (deflateInit2 (strm, Z_DEFAULT_COMPRESSION, Z_DEFLATED,
windowBits | GZIP_ENCODING, 8,
Z_DEFAULT_STRATEGY));
}
/* Example text to print out. */
static const char * message =
"Shall I compare thee to a summer's day?\n"
"Thou art more lovely and more temperate:\n"
"Rough winds do shake the darling buds of May,\n"
"And summer's lease hath all too short a date;\n"
;
int main ()
{
unsigned char out[CHUNK];
z_stream strm;
strm_init (& strm);
strm.next_in = (unsigned char *) message;
strm.avail_in = strlen (message);
do {
int have;
strm.avail_out = CHUNK;
strm.next_out = out;
CALL_ZLIB (deflate (& strm, Z_FINISH));
have = CHUNK - strm.avail_out;
fwrite (out, sizeof (char), have, stdout);
}
while (strm.avail_out == 0);
deflateEnd (& strm);
return 0;
}